Wiring up heated front screen with a TOK switch

[AndyPen]

I've got a works wiring diagram but apart from the extra addition of a relay it isn't all that helpful. Can anyone add any clarity please? We can do it left and right but the old TOK switches were marked with increasing power ratings, not sides.

This is what we are working with - with thanks to one of our forum members for helping me out already

heated screen.jpg

TOK switch.jpg

[Ronnie]

The works TOK switch was never marked with any power ratings Andy It should be marked 1,1a,1b and 2 and it switches the earth & power circuits to alternate between series or parallel through the screen bus bar's.

[AndyPen]

Thanks Ronnie and perhaps my fault for not being clearer, the Tok one are indeed marked that way, but the markings I meant are the ones on the dash, as per the works cars. Bit like this example

dash example.jpg

heated screen works wiring.jpg

[Ronnie]

Thanks Ronnie and perhaps my fault for not being clearer, the Tok one are indeed marked that way, but the markings I meant are the ones on the dash, as per the works cars. Bit like this example

What is the part # on your switch (supplier any instructions) From your picture it looks correct, but internals can differ.

1/4 Power power goes in O/S earth is through N/S 2.36 Amps.
1/2 Power (drivers side) power in O/S earth centre 4.66 Amps.
Full Power power in both sides earth centre 10 Amps. all ratings Triplex screen.

[AndyPen]

Thanks Ronnie and perhaps my fault for not being clearer, the Tok one are indeed marked that way, but the markings I meant are the ones on the dash, as per the works cars. Bit like this example

What is the part # on your switch (supplier any instructions) From your picture it looks correct, but internals can differ.

1/4 Power power goes in O/S earth is through N/S 2.36 Amps.
1/2 Power (drivers side) power in O/S earth centre 4.66 Amps.
Full Power power in both sides earth centre 10 Amps. all ratings Triplex screen.

Thanks ever so much for your help here Ronnie. I have yet to find a part number and am wondering where to look???

Here are a few more pics, the terminals are 1, 1A and 1B in the visible pics, and I can check that the 2 is on the underside when I go back to my unit where the car is.

Screenshot 2022-07-24 at 10.38.26.jpg

Screenshot 2022-07-24 at 10.37.20.jpg

Screenshot 2022-07-24 at 10.36.41.jpg

[Oneball]

Just get a multimeter out and see which terminal corresponds to which switch position. It’s just a four position switch. It isn’t a variable resistor. The power is controlled by which route the current takes through the screen as per Ronnie’s instructions.

[Ronnie]

Thanks Ronnie and perhaps my fault for not being clearer, the Tok one are indeed marked that way, but the markings I meant are the ones on the dash, as per the works cars. Bit like this example

What is the part # on your switch (supplier any instructions) From your picture it looks correct, but internals can differ.

1/4 Power power goes in O/S earth is through N/S 2.36 Amps.
1/2 Power (drivers side) power in O/S earth centre 4.66 Amps.
Full Power power in both sides earth centre 10 Amps. all ratings Triplex screen.

Thanks ever so much for your help here Ronnie. I have yet to find a part number and am wondering where to look???

Where did it come from I can tell you how to wire a ToK P13-1 7530 which is what I was supplied by S/T in 1972 and Identical to the one in my rally car, also it is the switch that was intended for the operation of the heated screen in competition instead of the NSF Timer used for consumer use (AA1000):?: Yours is a newer version with all the terminal ports in the laminates. I will send instructions by PM if you want, just incase I blow lots of Lucas smoke all over the internet. Let me know

[AndyPen]

Thanks as ever to everyone on the forum for you excellent help. Hoping my electrical guru can come over and sort this later in the week. He is more familiar with slightly later cars like his rally TRV8 - so help is very much appreciated.

[m1cH1]

Well, how to wire up a TOK switch for a heated front screen? That is a question I had myself some time ago!
Back then (I think,it was in 2019), I did think about it for some time, because I also wanted to understand the ¼/½/Full Power labeling.

After finding two different excerpts from "works" wiring diagrams, as well as a schemtic by Minispares for their MS86/"works spec" heated front screen and then some thinking, I´ve drawn up the different switching configurations. The red lines show continuity for each switched position:

TOK_wiring_characteristics.png

Having drawn up the switching configurations, I started to grasp why they labelled it the way they did. While in "½ Power" only the drivers side gets heated, only the two other switching positions heat both halves of the screen. When selecting "¼ Power", in series. And when selecting "Full Power", in parallel. And that makes a huge difference in regards to the effective resistance and thus the current that is flowing through the heating elements and then beeing dissipated as heat.
A better labelling of the switch would probably be "Off" / "Driver Only" / "Full screen: low" / "Full screen: high".
But I fear the labelling was probably done by an engineer...

For all of you that might want to see, if the ¼/½/Full Power labeling is right, I´ve then put on my "engineering hat" and wrote it down, in detail.
I hope my train of thought in the text below can be followed to a sufficient extent...

Cheers, Mike

TOK_power_considerations.png

[m1cH1]

Oh and as I´ve just seen that Andy mentioned the relay. A small addendum regarding that:

It is just there to ensure that the TOK switch can only be switched, when ignition is "on".
The winding (W1/W2) gets excited by a fused auxiliary circuit (green wire), that is fed through the ignition switch.
It then closes the contacts (C1/C2) and allows operation of the TOK switch and thus the heated front screen.

[m1cH1]

Oh, and I forgot that I had created a layer with the wiring in colour. It was just turned off / hidden and I missed it when exporting...

TOK_Wiring_Colour.png

[AndyPen]

Wow, what can I say, how comprehensive is that!!!

Many many thanks for sharing, it is the icing on the cake

[mk1]

Thanks Mike, a perfect explanation